Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$90.43	11.581%	$100.9027	$100.90	$100.90	$100.90
Purchase #2	$44.51	11.360%	$49.5663	$49.57	$49.55	$49.60
Purchase #3	$110.48	10.418%	$121.9898	$121.99	$122.00	$122.00
Purchase #4	$118.48	6.727%	$126.4501	$126.45	$126.45	$126.50
Purchase #5	$35.39	9.816%	$38.8639	$38.86	$38.85	$38.90
Purchase #6	$190.34	13.705%	$216.4261	$216.43	$216.45	$216.40
Purchase #7	$139.84	5.401%	$147.3928	$147.39	$147.40	$147.40
7 purchase totals =	$729.47		$801.5917	$801.59	$801.60	$801.70